1. Field of the Invention
The present invention relates to a high temperature stable ohmic contact electrode. More specifically, the present invention concerns a method for manufacturing a semiconductor device using a self-alignment process ion implantation with such a high temperature stable ohmic contact electrode and a semiconductor device manufactured by this method, including a bipolar transistor device and a field effect transistor device.
2. Description of the Related Art
An ohmic contact electrode of metal molybdenum to GaAs (a III-V compound semiconductor) through a germanium layer is known, but to make an ohmic contact in this electrode, annealing for reacting the germanium with GaAs is necessary and an alloy layer formed by the annealing cannot be precisely controlled, and thus the problem of nonuniform element characteristics arises.
As an ohmic contact electrode which solves the above problem, there is known an electrode in which tungsten silicide WSi is formed on a GaAs layer through a single crystalline germanium layer. This electrode is ohmic to GaAs without annealing and does not have the problem of the above-mentioned electrode (Japanese Unexamined Patent Publication (Kokai) No. 60-10776).
The electrode described in Japanese Unexamined Patent Publication (Kokai) No. 60-10776 has an advantage in that an ohmic contact is obtainable to GaAs without annealing, but this is not stable at a high temperature and the ohmic characteristic is deteriorated by annealing the ion implanted region for activation after the formation of the electrode. Accordingly, when an ion implanted region is formed in self-alignment with the electrode as a mask, the electrical resistance thereof is increased, which is a problem.
The ohmic contact of this electrode is not stable at a high temperature because, while the ohmic contact to the germanium layer is provided by doping arsenic As at a high concentration, the arsenic, which is highly volatile, is released by the annealing to deteriorate the ohmic contact of the electrode.